Callaway E M, Wiser A K
Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
Vis Neurosci. 1996 Sep-Oct;13(5):907-22. doi: 10.1017/s0952523800009159.
We studied excitatory local circuits in the macaque primary visual cortex (VI) to investigate their relationships to the magnocellular (M) and parvocellular (P) streams. Sixty-two intracellularly labeled spiny neurons in layers 2-5 were analyzed. We made detailed observations of the laminar and columnar specificity of axonal arbors and noted correlations with dendritic arbors. We find evidence for considerable mixing of M and P streams by the local circuitry in VI. Such mixing is provided by neurons in the primary geniculate recipient layer 4C, as well as by neurons in both the supragranular and infragranular layers. We were also interested in possible differences in the axonal projections of neurons with different dendritic morphologies. We found that layer 4B spiny stellate and pyramidal neurons have similar axonal arbors. However, we identified two types of layer 5 pyramidal neuron. The majority have a conventional pyramidal dendritic morphology, a dense axonal arbor in layers 2.4B, and do not project to the white matter. Layer 5 projection neurons have an unusual "backbranching" dendritic morphology (apical dendritic branches arc downward rather than upward) and weak or no axonal arborization in layers 2-4B, but have long horizontal axonal projections in layer 5B. We find no strong projection from layer 5 pyramidal neurons to layer 6. In macaque V1 there appears to be no single source of strong local input to layer 6; only a minority of cells in layers 2-5 have axonal branches in layer 6 and these are sparse. Our results suggest that local circuits in V1 mediate interactions between M and P input that are complex and not easily incorporated into a simple framework.
我们研究了猕猴初级视觉皮层（V1）中的兴奋性局部回路，以探究它们与大细胞（M）和小细胞（P）通路的关系。对2-5层中62个细胞内标记的棘状神经元进行了分析。我们对轴突分支的层状和柱状特异性进行了详细观察，并注意到其与树突分支的相关性。我们发现有证据表明，V1中的局部回路使M和P通路发生了大量混合。这种混合由初级膝状体接受层4C中的神经元以及颗粒上层和颗粒下层中的神经元提供。我们还对具有不同树突形态的神经元的轴突投射可能存在的差异感兴趣。我们发现，4B层的棘状星状神经元和锥体细胞具有相似的轴突分支。然而，我们识别出了两种类型的5层锥体细胞。大多数具有传统的锥体细胞树突形态，在2、4B层中有密集的轴突分支，并且不投射到白质。5层投射神经元具有不寻常的“反向分支”树突形态（顶端树突分支向下而非向上），在2-4B层中轴突分支较弱或没有轴突分支，但在5B层中有长的水平轴突投射。我们发现5层锥体细胞向6层没有强投射。在猕猴V1中，似乎没有单一的强局部输入源到6层；2-5层中只有少数细胞在6层中有轴突分支，并且这些分支很稀疏。我们的结果表明，V1中的局部回路介导了M和P输入之间复杂且不易纳入简单框架的相互作用。
